Method for detecting misfiring in a multi-cylinder internal combustion engine

ABSTRACT

The present invention relates to a method for detecting combustion misses in a multi-cylinder internal combustion engine, having at least one first engine control unit which controls at least the injection and firing of a first subset of the cylinders of the internal combustion engine, and having at least one further engine control unit which controls the injection and firing of a further subset of cylinders and in which the detection of combustion misses for the first and the further subset of cylinders is additionally carried out; the control units using an engine control program which is interrupted by interrupt routines, in phase-synchronism with the rotational movement of the crankshaft, in which at least the data required for the injection and firing are processed; and in which method the detection of combustion misses is based on establishing and evaluating crankshaft segment times in which the crankshaft covers an associated circle-segment angle range; and the crankshaft segment times likewise being established and evaluated in particular interrupt routines, the crankshaft segment times being established and evaluated for the further subset of cylinders in the interrupt routines in which their firing is controlled, and the crankshaft segment times for the first cylinder being established and evaluated in certain additionally generated interrupt routines.

[0001] The present invention relates to a method for detectingmisfirings in a multi-cylinder internal combustion engine having thefeatures indicated in the preamble of Claim 1.

BACKGROUND INFORMATION

[0002] Methods for detecting combustion misses having the featuresaccording to the species are generally known from the related art. Themethods are essentially based on a comparison of values determinedinternally within the engine and pertaining to the irregular running ofindividual cylinders of the internal combustion engine to definedthreshold values, and inferring a combustion miss in those cases wherethe detected irregular running values exceed the threshold value.

[0003] The irregular running values of individual cylinders relevant fordetecting combustion misses are obtained by exploiting the knowledgethat, in contrast to normal operation, an absent or incompletecombustion within a cylinder causes characteristic changes in the torquecurve of the engine. By comparing the torque curves, i.e. thecontribution made to the torque by individual cylinders, a distinctioncan then be made between normal, misfire-free operation of the internalcombustion engine and the operation in which misfires occur. Thedifferences in the torque characteristic are determined by calculatingsegment times, taking into account that a lower torque contribution,resulting from a misfire, causes longer segment times of the crankshaft,one crankshaft segment in each case corresponding to the piston movementof individual cylinders during the torque-producing expansion phase. Thecrankshaft segment times may be sampled via appropriate sensors, forinstance at a trigger wheel mounted on the crankshaft or camshaft, onwhich the limits of the segment areas are marked. The crankshaft segmenttimes are usually determined in synchronism with the firing and storedand analyzed in engine control units. In this case, the evaluation iscarried out by calculating irregular running values from the determinedcrankshaft segment times, the irregular running values allowing thedetection of combustion misses through a comparison of a setpoint valuewith a threshold value, where the exceeding of the established thresholdvalue is interpreted as a combustion miss in the associated cylinder.

[0004] The described method for detecting combustion misses hasgenerally been useful in the case of multi-cylinder internal combustionengines having a central engine control unit. However, in the case ofengines having a high number of cylinders and a plurality of controlunits, the problem arises that the evaluation of irregular runningvalues from consecutive segment times is extremely complicated, due tothe fact that each control unit only serves a number of cylindersconnected thereto, with only data from a subset of ignition outputstages and fuel injectors being processed in each of the control units.Because the cylinders are distributed among a plurality of controlunits, the irregular running values from consecutive segment times canonly be determined by a corresponding investment in memory andcalculation and used for the detection of misfirings.

[0005] Furthermore, problems may occur in computing time.

[0006] For the purpose of illustration, an engine having two controlunits is considered, each controlling the firing and injection of onegroup of cylinders each, and in which the detection of combustion missesis integrated into one control unit. Hereinafter this control unit isalso referred to as a diagnostic control unit.

[0007] The present invention distinguishes itself by an advantageousdivision of the computing time of the diagnostic CU between two firingswithin the cylinder group associated with this control unit.

[0008] In principle, the time interval between two such firings issufficient to process the data from the first firing, to generate anadditional interrupt which is assigned to a firing of the other controlunit, to detect an associated segment time and to process it fordetecting combustion misses.

[0009] Not only is an evaluation of the associated segment times fordetecting misfires carried out in the interrupt routines of thecylinders whose firings are controlled by the diagnostic control unit.In addition, further functions, such as firing and fuel injection, arealso calculated within the framework of these routines.

[0010] In contrast, in the routines of the interrupt, which areallocated to the firings of the other cylinders that are calculated bythe second control unit, only segment times are detected and evaluatedfor the detection of combustion misses.

[0011] For that reason, the interrupt routines of the cylinderscontrolled by the diagnostic control unit are considerably longer in thetime characteristic than those of the cylinders that are controlled bythe second control unit.

[0012] It is problematic that the processing of the data from the firstfiring may require so much time that the further interrupt, givencomplete processing of the data from the first firing, does not occur insynchronism with the firing interrupt of the second control unit.

[0013] If the processing of the data from the first interrupt isinterrupted and if precedence is given to the further interruptoccurring in synchronism, including calculation of its data, it mayoccur that the calculation results of the further interrupt areavailable before the calculation results of the first interrupt. In sucha case, undesirable switches in the calculation sequence of theirregular running may result.

[0014] According to the present invention, the processing of data fromthe first firing is interrupted in order to trigger the furtherinterrupt; after triggering the further interrupt, the associatedsegment time is detected in correct phase relation to the firinginterrupt of the second CU and stored.

[0015] Thereupon,. the processing of data from the first firing is firstcompleted before the irregular running value is calculated with the aidof the segment time of the further interrupt.

[0016] In this manner, it is advantageously assured that the irregularrunning value from the first firing is always present in the CU beforethe irregular running value from the immediately following firinginterrupt of the second CU. Switches in the order or calculation of theirregular running are thereby avoided.

[0017] A further important advantage is that, due to the additionalinterrupts for those cylinders that are not connected to the diagnosticCU, the algorithm for detecting combustion misses, and thus the softwareimplementation for designs having two control units, may largelycorrespond to the software implementation for one-control unit design.

[0018] Reason: The software used to evaluate the segment times isrunning in both interrupts, i.e., in the interrupts of the connected,and in the interrupts of the unconnected cylinders. If only theinterrupt of the connected cylinders were present, the algorithm fordetecting combustion misses and/or the software implementation fortwo-CU designs would need to be fundamentally changed, since segmenttimes for two firings would then have to be analyzed within oneinterrupt routine.

[0019] With the aid of the additional interrupts, the running time ofthe interrupt routines of the connected cylinders may be shortened.

[0020] The design approach according to the present invention disclosesin detail a method for detecting combustion misses in a multi-cylinderinternal combustion engine having at least one first engine controlunit, which controls at least the injection and firing of a first subsetof the cylinders of the internal combustion engine; and having at leastone additional engine control unit (diagnostic control unit), whichcontrols the injection and firing of a further subset of cylinders andin which the detection of combustion misses for the first and thefurther subset(s) of cylinders is also carried out; the control unitsusing an engine control program which is interrupted inphase-synchronism with the rotational movement of the crankshaft byemploying interrupt routines in which at least those data are processedthat are required for the injection and firing. Furthermore, in thismethod the detection of combustion misses is based on establishing andevaluating crankshaft segment times in which the crankshaft covers anassociated circle-segment angular range, and the crankshaft segmenttimes likewise being established and evaluated in certain interruptroutines, the crankshaft segment times for the further subset ofcylinders being established and evaluated in the interrupt routines inwhich their firings is controlled, and the crankshaft segment times forthe first cylinders being established and evaluated in certain,additionally generated interrupt routines.

[0021] In those cases where the crankshaft segment time of one of thefirst cylinders must be detected in phase-synchronism with the enginerotation, and the interrupt routine of the further cylinder previous inthe firing sequence is not yet completed, in one advantageousembodiment, the incomplete interrupt routine of the further cylinderprevious in the firing sequence is interrupted, the crankshaft segmenttime of the one of the first cylinders is detected and stored, theincomplete interrupt routine of the further cylinder previous in thefiring sequence is processed, and only then is the crankshaft segmenttime of the one of the first cylinders processed for the detection ofcombustion misses.

Advantages of the Invention

[0022] The method of the present invention for detecting combustionmisses in multi-cylinder internal combustion engines having the featuresas recited in Claim 1 has the advantage over the known related art thata reliable detection of combustion misses may be ensured, even whenusing at least two engine control units, each processing data from asubset of the cylinders for firing and injection during the operation ofthe internal combustion engine; no complicated data detection and dataevaluation in different control units are required. Since the crankshaftsegment times needed for detecting combustion misses are detected,stored and evaluated in one of the engine control units for all ofcylinders of the internal combustion engine, no data transfer betweenindividual engine control units is required any longer. The detection,storing and evaluation of the crankshaft segment times are carried outin the relevant control unit, first of all, by generating firinginterrupts of the cylinders connected to the control unit, and,secondly, by generating mathematically calculated interrupts, occurringin time between these firing interrupts, for those cylinders which areassigned to one or more other engine control units. By this measure, thesegment times of consecutively occurring firings are available in onecontrol. unit for the algorithm used in misfire detection throughevaluation of the irregular running of individual cylinders, and can beevaluated in this manner without any problem.

[0023] The interrupt(s) determined arithmetically, occur duringgeneration in the control unit which is used to detect combustionmisses, simultaneously with the firing interrupts of the particularcontrol unit which controls the instantaneously firing cylinder.

[0024] Particularly advantageous embodiments of the method according tothe present invention result from an overall view of the technicalteachings in Claim 1 with the features of the subclaims.

[0025] In order to ensure that the calculation sequence of thecombustion miss detection is not mixed up during the interruption of thefiring interrupt by the mathematically calculated, additionallygenerated interrupt, it has proven useful if the mathematicallygenerated interrupts interrupt the actual firing interrupt only in orderto establish and store the segment time. Processing of the data of themathematically generated interrupt is only carried out after completeprocessing of the data from the normal firing interrupt. Thus, themethod according to the present invention makes it possible to implementthe calculation sequence for detecting combustion misses in one of theengine control units, independent of the number of engine control unitsused for the control of an internal combustion engine, so that themethod of the present invention is universally applicable.

DRAWING

[0026] Hereinafter, the sequences of the method according to the presentinvention, especially as they pertain to the generation of firinginterrupts and mathematically generated interrupts, as well as the timesequence for the segment times required in the detection of combustionmisses, are explained with the aid of a schematic flow chart. In theincluded drawing, the sequence is shown using the examples of a designhaving two control units.

DESCRIPTION OF THE METHOD ACCORDING TO THE PRESENT INVENTION

[0027] In the included drawing, a horizontal time line is depicted anddesignated as “t”. Above this time line t, three firing interruptsgenerated inside an engine control unit are marked by vertical notations1, 2 and 3, each of firing interrupts 1, 2 and 3 corresponding to one ofthe ignition pulses, controlled by the control unit in question, of acylinder assigned to this control unit. Between firing interrupts 1, 2and 3 in the drawing can be seen designations 4 and 5, which indicatethe moment of mathematical interrupts, the moments of the mathematicalinterrupts conforming with the firing interrupts generatedsimultaneously in the other control unit of the respective cylinderconnected thereto. Not only after the firing interrupts, but also afterthe mathematical interrupts generated in between, a time span t6 can beseen from the FIG., during which the crankshaft segment time, which isrequired as a base value for the combustion miss detection, isascertained and stored. When viewing the time span between firinginterrupt 1 and firing interrupt 2, it becomes clear from the FIG. thatfirst, after calculation and storing of the segment time during timespan t6, the data processing of the firing-synchronous interrupt iscarried out within an ensuing time span t7. Time span t7 is interruptedonce in order to detect and store the segment time of mathematicallycalculated interrupt 4. As can be seen from the FIG., the time spanbetween two sequentially occurring firing interrupts 1 and 2 is longerthan actual data processing time span t7. Thus, a time span t8 remainsbetween the end of processing time t7 and the next firing interrupt,during which the evaluation of the segment time associated withmathematically calculated interrupt 4 can be carried out. Consequently,while the time span of the firing interrupt is interrupted by themathematically determined interrupt, this only occurs in order toestablish and store the segment time. The processing o themathematically calculated interrupts is carried out only after thecomplete processing of the actual firing interrupt.

What is claimed is:
 1. A method for detecting combustion misses in amulti-cylinder internal combustion engine, having at least one firstengine control unit which controls at least the injection and firing fora first subset of the cylinders of the internal combustion engine, andhaving at least one additional engine control unit which controls theinjection and firing of a further subset of the cylinders and in whichthe detection of combustion misses for the first and further subset ofcylinders is also carried out; the control units using an engine controlprogram which is interrupted by interrupt routines, in phase-synchronismwith the rotational movement of the crankshaft, in which at least thedata required for injection and firing is processed; and in which methodthe combustion miss detection is based on the establishment andevaluation of crankshaft segment times in which the crankshaft covers anassociated circle-segment angle range, and the establishment andevaluation of the crankshaft segment times likewise being carried out inspecific interrupt routines; the establishment and evaluation of thecrankshaft segment times for the additional subset of cylindersoccurring in the interrupt routines in which their firing is controlled,and the establishment and evaluation of the crankshaft segment times forthe first cylinders being carried out in certain additionally generatedinterrupt routines.
 2. The method as recited in claim 1, wherein, in thecase that the crankshaft segment time of one of the first cylinders mustbe detected in phase-synchronism with the engine rotation and theinterrupt routine of the further cylinder previous in the firingsequence is not yet completed, the still incomplete interrupt routine ofthe further cylinder previous in the firing sequence is interrupted, thecrankshaft segment time of the one of the first cylinders is detectedand stored, the incomplete interrupt routine of the further cylinderprevious in the firing sequence is completed, and only then is thecrankshaft segment time of the one of the first cylinders processed fordetecting combustion misses.